1. The Field of the Invention
The present invention relates in general to a transfer type fabricating system capable of placing electronic components on circuit boards such as printed circuit boards while the circuit boards are transferred by a conveyor device or devices through the working stations, and more particularly to a device that complements such a transfer type fabricating system to improved the efficiency thereof.
2. The Relevant Technology
The electronic industry is characterized by short product life spans or, at least, by product life spans having varying magnitude. Because of the high capitalization costs of dedicated assembly equipment, and because of short product life spans, dedicated assembly equipment is not particularly useful for the assembly of electronic components in small lots. Because of these difficulties with dedicated electronic assembly equipment, variable, programmable assembly techniques are now being widely utilized for the placement and assembly of electronic components on printed circuit boards.
Various machines and methods for the placement of electronic components in a circuit board are known in the prior art, including those disclosed in U.S. Pat. Nos. 5,696,292 and 5,044,069, each of which are issued to Assai et al., assigned to Fuji Machine Mfg. Co., Ltd., and incorporated herein by reference.
One example of a transfer type circuit board fabricating system includes a plurality of modules arranged in series. The first module can be a loading module that includes a conveyor device which is adapted to receive a printed circuit board (PC board) from a downstream fabricating assembly, and load the PC board onto another module which may apply a solder material to the PC board. The PC board is then moved to yet another module for the picking of electronic components and the placement of the same on the PC board. This module is often called `pick and place` or a `chip placer`, an example of which is found in the Fuji CP-642 distributed by Fuji America Corporation located in Vernon Hills, Ill., USA.
In the pick and place module, a component placer head is movable within an area to retrieve a selected electronic component from a component supply device which accommodates a roll of a component carrier tape. The tape holds a multiplicity of electronic components or chips and has multiple recesses which are open in one of the opposite surfaces of the tape and which are spaced apart from each other in the longitudinal direction of the tape at a predetermined spacing interval. The recesses accommodate respective electronic components and are closed by a covering or waste tape.
In operation of the component supply device, the component carrier tape is intermittently fed by a suitable feed device from the roll at a pitch corresponding to the spacing interval of the component accommodating recesses of the tape. As the component carrier tape is fed, the covering or waste tape is removed to permit an access to the electronic components contained in the recesses, so that these components are successively fed one after another to a predetermined supply position. Suction from a nozzle mounted on a turret is used to pick a selected electronic component from a recess in the tape. The turret is then rotated so that the nozzle is in a position such that the nozzle can place the selected electronic component into desired location on a particular PC board.
A heating furnace as well known in the art is disposed downstream of the pick and place module and is used to heat the solder so as to fix the placed electronic components to the PC board.
In yet another example of an assembly of machines for producing a circuit board such as a printed circuit board, a number of working modules are required for programmably assembling PC boards. These working modules are configured in an assembly line, with each working module being utilized for fixing a certain subset of components to a particular PC board. A linear conveyor transports a circuit board along the assembly line from one working module to the next. In the assembly line, the circuit board is generally subjected to various operations such as: application of a creamy solder by screen printing to local portions of the substrate at which electronic components are placed; application of an adhesive material to those portions of the substrate; placement of electronic components on the substrate; and heating the creamy solder in an oven to fix the electronic components to the substrate.
An unloading module can be located downstream of a succession of the plurality of working modules as viewed in the predetermined transfer direction. The unloading module includes a conveyor device for removing the circuit boards from one of the working modules located at a downstream end. The circuit boards on which the intended operations in all the working modules have been completed are automatically removed by the unloading device from the system.
Each working module can include a component placing device for placing electronic components on the circuit boards, and a component imaging device for obtaining image data representative of an attitude of each of the electronic components when each electronic component is held by the component placing device. The component imaging device can also detect a dropped or missing electronic components prior to mounting onto a printed circuit board.
With programmable assembly techniques, one working module uses robotic means for selecting individual electronic components from a storage area and for transporting those selected components to an assembly station. At the working module, the robotic means properly locates the components with respect to the printed circuit board. Because the robotic means can be programmable, various circuits may be assembled, and the high capital cost of dedicated assembly equipment is avoided as well.
In the case of the robotic means or component placing device arranged to place electronic components or chips on a substrate or PC board, the placing device includes a placer head for placing the components on the substrate, a three-dimensional positioning device for positioning the placer head along three axes, and a controller for controlling the placer head and positioning device. The component placing device usually has a placer head which holds the electronic component and which is positioned to place the electronic component at the desired position on the circuit. A vacuum pump is used for operating the placer head of the component placing device to hold the electronic component by vacuum suction, for example.
The electronic components to be placed on the circuit boards by the component placing device may be optionally coated with a suitable fixing material for provisionally fixing the electronic components on the circuit boards. To prevent dislocation of the electronic components, it is desirable to provisionally fix the electronic components on the circuit boards. To this end, the electronic components are coated with the fixing material, by contacting the electronic components with the material held by the material holder, before the electronic components are placed on the circuit boards. Thus, the electronic components are provisionally fixed on the circuit boards. The fixing material may be a flux or a liquid agent. Where the electronic components are fixed by a solder on the circuit boards, the solder is melted by heat application in a suitable heating furnace at another working module, so that the electronic components are permanently fixed or bonded to the circuit boards by the solder. In this respect, it is noted that the electronic components placed on the circuit boards may be dislocated from the nominal positions, while the circuit boards are transferred with the electronic components into the heating furnace.
One system for supplying electronic components for placement on the PC board involves the accommodation of electronic components in component supply pallets in a pallet storage. A pallet support block and the pallet storage are moved by a first moving device relative to each other so that a pallet rack supporting the component supply pallet which accommodates the electronic components to be placed on the appropriate circuit board has the same height as the pallet support block. Then, the pallet supply pallet in question is moved by a second moving device onto the pallet support block. The component placing device receives the electronic components one after another from the component supply pallet placed on the pallet support block, and places the received electronic components on the circuit board. The component supply device which uses the component supply pallets as described above is suitable to supply the electronic components which have comparatively large sizes or specially-shaped electronic components such as connectors and sockets.
The conveyor device of each of the plurality of working modules includes a plurality of conveyors which are disposed in series in the predetermined transfer direction of the circuit boards. In this case, the loading and unloading of the electronic components onto and out of the present fabricating system may take place at different times. That is, an unloading operation to remove the circuit board on which the electronic components have been placed and a loading operation to introduce the circuit board on which the working operations are to be performed may take place at different times, so that the fabricating system provides increased operating flexibility and efficiency.
A random access surface mounted component transport system used in the population of components in PC board fabrication may include an elongated movement mechanism including a multiple component carrier. The mechanism can have a plurality of adjacent loading points and a downstream off-loading station, where there are a plurality of adjacent component carrier media that are disposed adjacent the movement mechanism. Each component carrier media is associated with a different one of the loading points.
Despite their success, a number of problems remain with prior art programmable PC board assembly techniques utilizing robotic means for the placement of electronic circuit components on substrates or printed circuit boards. Typical printed circuit boards require the placement of a large number of differing components with respect to a single circuit board. Space constraints, however, limit the number of differing components which may be assembled on a given substrate or circuit board with a given robotic assembly machine. Space constraints may be increasingly severe as the number of electronic components to be placed on a PC board increases. With the increase in the number and diverse sizes and shapes of electronic components to be placed on a PC board, problems may occur. These problems are inherent in the difficulty of robotic placement of the electronic components. One such problem is the improper placement or dropping of electronic components during the pick and place operation.
Another problem, which is further complicated by the foregoing problem, is the difficulty caused by a loss of attachment between a placer head of a component placing device and an electronic component which is to be positioned and placed at a desired position on the circuit. Such a loss could be, for example, a loss of in the vacuum force between the electronic component and a nozzle applying the vacuum thereto. Loss of vacuum or other attachment force causes the electronic component held by the place head to fall from the placer head. The place where the fallen electronic component ends up will undoubtedly be other than a respectively proper sites on the printed circuit board.
Particularly troublesome is the problem of the electronic component falling to a resting place that is not easily accessible to maintenance personnel. It is even more problematic that, after a period of time, an accumulation of fallen electronic components can cause a malfunction of the working module of the linear conveyor that transports circuit boards along the assembly line from one working module to the next. A prolonged and expensive maintenance procedure must then be taken that ultimately reduces throughput of the PC board assembly line. It would be an advance in the art of electronic component placement devices and techniques to provide apparatuses and methods that limit or otherwise prevent fallen electronic components from ending up at or accumulating in inaccessible locations that are problematic to such electronic component placement devices and techniques. Such apparatuses and methods are disclosed and claimed hereinafter.